Certain integrated circuits (ICs) that are designed to handle large amounts of current are often limited to low pin-count packages. Typically, such devices have only 5, 7, or 9 leads along a single side of the IC. A heat sink typically occupies an entire face of the package and is often capable of being attached to a much larger system heat sink for cooling purposes. It is the size and mounting requirements of the heat sink that precludes an electronics designer from using all sides of the IC package for external signal routing.
The same power handling criteria require that at least some of the IC leads be larger than normal. The voltage supply, ground and output leads in particular must be oversize to avoid unnecessary voltage drops. The combined effect of the heat sink and the oversize leads severely limits the number of pins mountable on such an IC.
ICs that process microwave signals have problems with similar results. There, problems of lead inductance and capacitance mandate few pins.
The electronics market is driving, and will continue to drive, the complexity of high current ICs to greater and greater levels. The engineering problems described above, however, limit the number of pins and, hence, the potential complexity of the external interface of a high IC current. The result of this juxtaposition is that the IC design engineer must attempt to control a certain number of parameters through a small number of input pins. A high current 7-pin IC, for instance, only has two available pins once the input, output, power supply, ground, and fault signals are taken into account. These two pins and the input pin must control all of the operating parameters of an IC. The input pin customarily receives a logic on-off signal leaving the two remaining pins to handle all analog programming. The two pins, for instance, must control the pull-in current, pull-in time, and hold-in current when a 7-pin IC acts as a solenoid controller.
One solution would be to input control parameters into a system through two pins using a serial interface with digital encoding. Such a solution, however, would not be economically feasible in most instances.
Therefore, a need has arisen for an integrated circuit interface which is able to economically control a plurality of operating parameters with a limited number of package pins.